Arrangements for producing electric oscillations of very high frequency



Dec. 24, 1968 B. a. VAN IPEREN E L 3,418,516

ARRANGEMENTS FOR PRODUCING ELECTRIC OSCILLATIONS OF VERY HIGH FREQUENCY Filed Jan. 17, 1966 v INVENTORS BERNARDUS B.VAN IPEREN wnewus KUYPERS AGENT H United States Patent 3,418,516 ARRANGEMENTS FOR PRODUCING ELECTRIC OSCILLATIONS 0F VERY HIGH FREQUENCY Bernardus Bastiaan van Iperen and Wilhelmus Knypers, Emmasingel, Eindhoven, Netherlands, assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Jan. 17, 1966, Ser. No. 520,970 Claims priority, application Netherlands, Feb. 11, 1965, 6501676 4 Claims. (Cl. 315-553) ABSTRACT OF THE DISCLOSURE A sum-millimeter R-F generator including a resonant cavity which is excited in the TE mode, one end of which is provided with a tuning device and the other end being coupled to a waveguide which is angularly displaced with respect to the resonant cavity.

The invention relates to an arrangement for producing electric oscillations of a frequency higher than 300 gc. (wavelength smaller than 1 mm.). More particularly the invention relates to a device including a resonant cavity which is excited in the TE mode one end of which is provided with a tuning device and its other end is coupled by means of an aperture with a wave-guide extending in its longitudinal direction (Z-direction), while in the direction of height (X-direction) an electron beam modulated, for example, in density passes through the resonant cavity. The invention particularly relates to the manner in which a wave-guide is coupled with a resonant cavity for a wave-length of 0.5 mm. or smaller, which resonant cavity does not exhibit any re-entrant parts, and to a frequency multiplier provided with such a resonant cavity.

The resonant cavity may form part of a velocity modulation tube which comprises means for producing an electron beam which is focussed by a magnetic field and which passes from a cathode in order of succession at least through a modulation system, a drift space and an output system. In this event the output system comprises a rectangular resonant cavity preferably tuned to a higher harmonic. The wave-length of such a rectangular resonant cavity may in the longitudinal direction (Z-direction) be two or more half waves, while the width (Y- direction) may amount to one or more half waves. The height of the resonant cavity (X-direction) is generally smaller than the distance covered by an electron of the electron beam during a half period. Consequently, such a resonant cavity is excited in the TE mode.

A favorable structure is obtained if m=1 and n=2, in which event the resonant cavity is consequently excited in the TE mode.

The resonant cavity must not only be tunable, but it must also be coupled with an output wave-guide. This coupling is generally effected by means of an aperture which is narrower than the cross-section of the resonant cavity which is at right angles to the Z-axis. In an arrangement in which waves of wave-lengths of more than 1 mm. are produced, the narrowed aperture can be formed by the provision of ribs at the end of the resonant cavity, which ribs cause the transitional part between the resonant cavity and the wave-guide to be narrowed. In case of waves of approximately 1 mm., the mechanical tolerances are already so small, however, that for the structure the greatest possible accuracy of the processes is required. Below 0.5 mm., it is practically impossible to realize this structure.

In accordance with the invention it is possible to obtain a suitable coupling between the resonant cavity and the wave-guide also at wave-lengths of 0.5 mm. and smaller without the processes becoming too complicated and expensive. Thus, according to the invention the narrowed aperture for coupling the resonant cavity with the output wave-guide is obtained by turning the output wave-guide through a given angle with respect to the resonant cavity about its longitudinal axis which coincides with the Z-direction of the resonant cavity. The dimensions of the cross-section of the output wave-guide may be approximately equal to those of the cross-section of the resonant cavity at right angles to the Z-direction. The angle through which the output wave-guide must be rotated with respect to the resonant cavity is dependent upon the material of the resonant cavity and upon the ratio between the dimension in the X-direction and the resonance wave-length of the resonant cavity. Measurements and calculations have shown that in case of a resonant cavity of the said mode in which the dimension in the X-direction is one-sixth of the wave-length of the resonant cavity for a wave-length of 0.5 mm., the angle of rotation must be approximately 49 in order to obtain a match free of reflections between a resonant cavity provided in a copper body and the wave-guide. It is not necessary, of course, that the material of the wave-guide be copper.

The invention will now 'be described more fully with reference to the drawing in which:

FIG. 1 is a partly perspective sectional view of the arrangement in accordance with the invention, while FIG. 2 is a plan view of the coupling aperture between the resonant cavity and the wave-guide.

In FIG. 1, reference numeral 1 designates the resonant cavity for a wave-length of 0.5 mm. which terminates into the output wave-guide 2. Since the aperture of the Wave-guide 2 is rotated through an angle 6 (FIG. 2) with respect to the resonant cavity, a rhombic coupling aperture 7 is formed. Both the resonant cavity and the output wave-guide consequently each consist of a rectangular space which can be mechanically manufactured with required extremely small dimensions and with suflicient accuray. The wave-guide is closed in a vacuum-tight manner by means of the mica disc 6.

In the X-direction, a density-modulated electron beam 3 passes through the resonant cavity 1. At its upper end, the resonant cavity 1 terminates in a stepwise manner into a circular-cylindrical space 4 which is coupled with the resonant cavity comparatively unsatisfactorily. When a pin 5 having a flat end is displaced in the space 4, the frequency may be varied within a tolerance range of 5%.

This method of tuning has the advantage that the displacement of the pin 5 may be comparatively great so that the tuning becomes less critical.

The dimensions of a resonant cavity for a wave-length of 0.5 mm. (frequency 600 go.) are:

microns in the X-direction 460 microns in the Y-direction 600 microns in the Z-direction The length of the output wave-guide 2 (Z-direction) is not critical and may be 2 mm. The transverse dimensions of this wave-guide at right angles to the Z-direction are in this case approximately equal to those of the resonant cavity. The cavities are provided in copper bodies which are preferably connected with each other by diffusion.

While the invention has been described with reference to a specific embodiment and applications thereof, other modifications will be apparent to those skilled in this art without departing from the spirit and scope of the invention as defined in the claims.

What is claimed is:

1. An arrangement for producing electric oscillations having a wavelength of 1 mm. and shorter comprising a rectangular resonant cavity which is excited in the TE mode, a tuning device coupled to one end of said cavity, said cavity being coupled at its other end through a narrowed aperture with a rectangular output wave-guide extending in a given longitudinal direction, means to direct an electron beam through the resonant cavity in a given direction perpendicular to said longitudinal direction, said output wave-guide being rotated through a given angle with respect to the resonant cavity about an axis which coincides with said given longitudinal direction through the resonant cavity.

2. An arrangement as claimed in claim 1 in which the resonant cavity is excited in the TE mode.

4 3. An arrangement as claimed in claim 2 in which the electron beam is density modulated.

4. An arrangement as defined in claim 1 in which the resonant cavity is constituted by a hollow copper body.

References Cited UNITED STATES PATENTS 3,038,519 4/1962 Jepsen et a1. 3155.43 3,113,238 12/1963 Biechler et a1. 3l5-5.21 X

HERMAN K. SAALBACH, Primary Examiner.

SAXFIELD CHATMON, IR., Assistant Examiner.

US. Cl. X.-R. 

